A man has told a Sydney court he heard "deranged" and "incomprehensible" screaming before he saw a shirtless man throw an object off the balcony of The Hyde apartment building the morning Lisa Cecilia Harnum fell to her death.

Simon Gittany, 39, has pleaded not guilty to the murder of his fiancée, Ms Harnum, by causing her to fall from the couple's 15th storey rented apartment in the luxury building on Liverpool Street in Sydney's CBD on the morning of July 30, 2011.

At Mr Gittany's committal hearing on Tuesday, witness Josh Rathmell said he was walking through Hyde Park that morning when he heard screaming and looked up at the apartment building.

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"The best way I could [describe the screaming] would be emotional and deranged," Mr Rathmell told Downing Centre Local Court, via audio-visual link from New York.

"I believed it to be a male voice. It was deranged, it was incomprehensible."

Tragic ... the Hyde apartment building. Photo: Steven Siewert

Mr Rathmell said when he looked up at the building he saw a man throw a black object over the balcony.

"I saw a white male, I believe he had his shirt off, and my very first impression was this white male ... [had] something I could only guess at the time to be a black duffle bag or luggage.

"I believe I saw him in a rapid movement unload and move back."

He said the "unloading" motion and the man returning to the apartment was "one swift movement".

Mr Rathmell said he heard "two crashing sounds", and when he got closer to Liverpool Street, he saw people rushing towards the outside of the apartment.

"I started coming to the conclusion it's not a black object, but it was in fact a human being."

As he stood near Museum station, Mr Rathmell said he saw people trying to revive what he now realised was the body of a female.

He then saw a man, wearing a white shirt and striped pyjama pants, who he believed to be the man he'd seen on the balcony, approach the woman's body.

"I observed him openly mourning, obviously very shocked as he walked straight towards the body. He had his hands over his face.

"He then approached the body and knelt down beside it and engaged in conversation with people around him."

Mr Rathmell agreed with Mr Gittany's barrister, Anthony Bellanto QC, that he originally told police he was 50 metres away when he saw the incident, but told the hearing he was about 60 or 70 metres away.

"You agree first of all that there's an inconsistency about what you said in your statement ... about the distance you were away and what you said today," Mr Bellanto asked.

Mr Rathmell said: "That's correct. I've never been told exactly how far I was standing. All I can go off is just an approximate guess."